In an ad-hoc network environment in which various devices are connected to one another for use, pairing among the devices is a necessary factor. The ad-hoc network needs no base network device generally required for communication among devices constituting a network. That is, the ad-hoc network needs no a repeater among the devices constituting the network, such as a router or an AP (Access Point). The ad-hoc network can be established when a partial connection between devices constituting this network is performed, that is, pairing between a current specific device and another device is performed.
Recently, portable devices have been extensively used and communication using such portable devices has been increased more and more. Accordingly, the importance of an ad-hoc network, which enables communication among devices regardless of time and place even in an environment having no base network device for communication among devices, has been increased more and more. Data transmission between smart phones, screen coupling between a smart phone and a tablet or a smart TV, and the like may be an example of such an ad-hoc network.
In the ad-hoc network environment, since there is no base network device, the generation and management of a secret key to be used for communication security among devices are an important problem to be solved. In the ad-hoc network environment, since it is general that there is no trusted authority for distributing a secret key, a method for sharing the secret key among devices is very limited. Meanwhile, a RSA (Rivest Shamir Adleman) scheme, which is one of public key encryption schemes, has been extensively used for secure communication among devices. This algorithm uses two large decimals (normally, numbers of 140 digits or more), and one public key and the other one individual key are generated through a multiplication and an addition operation of these numbers. By using the generated public key and individual key, it is possible to encrypt and decrypt data that is used for communication.
However, the aforementioned RSA scheme is disadvantageous in that a calculation amount is large. In general, in order to generate a public key and an individual key in a Pentium-level computer, about 20 seconds to several minutes are required. Furthermore, the RSA scheme requires a large calculation amount for decryption. In addition, portable devices mainly used in the ad-hoc network are difficult to ensure a high computing capability due to problems of a battery, portability, and heat generation and the like. Therefore, the RSA scheme requiring a large calculation amount is not sufficient as a secure solution for the ad-hoc network.